542 U. S. BUEEAU OF FISHEBIES 



should be located at or near the low point of the coil, either inside 

 or outside the room, and the coils kept well flooded with ammonia, 

 with a trap to prevent the liquid ammonia from returning to the 

 compressor. The " flooding " of the pipes with liquid ammonia 

 secures the advantages of superior conduction of liquid in the coils 

 as compared with gaseous ammonia. The " flooded " system, how- 

 ever, requires certain features of design and installation that, for the 

 sake of safety, must not be overlooked. 26 



Where brine is used it is important to have a brisk circulation 

 forced by an efficient pump. A mistake in arrangement of the cir- 

 cuits of pipe may greatly reduce the efficiency of the freezers: 

 Where a main brine header is used, with many parallel circuits 

 branching off, the flow of brine may be rapid in the header but slow 

 in some rooms, especially when circuits in other rooms are open. 

 This difficulty is avoided if the circuits are all in series, or, if more 

 convenient, in two or three parallel series. When this arrangement 

 is made, a by-pass connection is made to bridge each room coil, so 

 that cutting off one room coil does not stop the flow through the 

 entire system. 



TEMPERATURE MAINTAINED IN SHARP FREEZERS 



It has already been pointed out that the more rapid the freezing 

 of fish the better. In fact, slow freezing is the one great defect 

 in the method of freezing now being described and which is in 

 common use. It is to be remembered also that the rate of freezing 

 is proportional to the difference in temperature between the fish 

 and their surroundings. If the fish on entering the freezer are 

 at 32° they will freeze 50 per rent faster at 16° below zero than 

 they will at 0°. The desirability of flooding the pipes with am- 

 monia or briskly circulating brine is therefore of as much impor- 

 tance as the degree of temperature of the ammonia or brine, good 

 insulation, and tight doors. 



In this connection it is desirable to define what we mean by tem- 

 perature of the air in the room. This temperature changes with 

 the opening of doors and the loading and unloading of the room. 

 When a freezer is filled with fresh fish and the door is closed the 

 temperature rises because the fish are giving up their heat to the 

 surrounding air. As the air warms, the difference between its tem- 

 perature and that of the brine pipes increases, and, according to 

 our rule, the rate of absorption of heat by the brine increases. The 

 brine, flowing at a constant rate, warms, and the difference between 

 its temperature and that of the ammonia increases, again giving up 

 heat faster, in accordance with the rule. The ammonia warms, and 

 the pressure shown by the suction gauge in the engine room rises. 

 These changes continue until the whole system is in equilibrium — 

 heat is being given up by the fish as fast as it is being absorbed 

 by the brine (or ammonia) in the pipes, and the machine removes 

 the heat at this same rate. The temperature in the sharp freezer 



28 See H. Rassbach, " The value of the flooded system, and its application to ice making 

 and refrigerating plants." Paper read before the American Society of Refrigerating 

 Engineers, Chicago, Oct. 18 and 19, 1909. Also published as Bulletin, L. A., by the 

 Vilter Manufacturing Co., Milwaukee, Wis. 



